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class="dropdown-item"><!----> <a href="/pages/28ec23/" class="nav-link">NAND Flash</a></li><li class="dropdown-item"><!----> <a href="/pages/62bf40/" class="nav-link">ARM 处理器</a></li><li class="dropdown-item"><!----> <a href="/pages/1a9374/" class="nav-link">嵌入式基础知识-存储器</a></li><li class="dropdown-item"><!----> <a href="/pages/aac5e3/" class="nav-link">闪存存储和制造技术概述</a></li><li class="dropdown-item"><!----> <a href="/pages/8f6056/" class="nav-link">芯片IO驱动力</a></li><li class="dropdown-item"><!----> <a href="/pages/d146b8/" class="nav-link">主流先进封装技术介绍</a></li><li class="dropdown-item"><!----> <a href="/pages/16f0ba/" class="nav-link">NAND Flash基础</a></li><li class="dropdown-item"><!----> <a href="/pages/90d8d0/" class="nav-link">基于PA算法的FTL引导</a></li><li class="dropdown-item"><!----> <a href="/pages/eb672b/" class="nav-link">SD逻辑擦除和物理擦除</a></li><li class="dropdown-item"><!----> <a href="/pages/747121/" class="nav-link">NAND Flash的SDR、ONFI、DDR接口</a></li><li class="dropdown-item"><!----> <a href="/pages/1eb351/" class="nav-link">【详解】Nand Flash必看知识</a></li><li class="dropdown-item"><!----> <a href="/pages/d2512a/" class="nav-link">【两万字详解】Nand Flash必看知识</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="面经" class="dropdown-title"><!----> <span class="title" style="display:;">面经</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d69946/" class="nav-link">虎牙C++技术面经</a></li><li class="dropdown-item"><!----> <a href="/pages/29251d/" class="nav-link">金山一面复习</a></li><li class="dropdown-item"><!----> <a href="/pages/c7c01f/" class="nav-link">完美世界秋招 C++ 游戏开发面经(Cpp部分)</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="其它" class="dropdown-title"><!----> <span class="title" style="display:;">其它</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/fa256e/" class="nav-link">博客搭建</a></li><li class="dropdown-item"><!----> <a href="/pages/335531/" class="nav-link">网站收藏箱</a></li></ul></div></div> <!----></nav></div></header> <div class="sidebar-mask"></div> <div class="sidebar-hover-trigger"></div> <aside class="sidebar" style="display:none;"><!----> <nav class="nav-links"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="CPP语言" class="dropdown-title"><!----> <span class="title" style="display:;">CPP语言</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/c5bdd8/" class="nav-link">Cpp之旅</a></li><li class="dropdown-item"><!----> <a href="/pages/279e62/" class="nav-link">Cpp专栏</a></li><li class="dropdown-item"><!----> <a href="/pages/801755/" class="nav-link">Effective_CPP</a></li><li class="dropdown-item"><!----> <a href="/pages/6b2468/" class="nav-link">muduo网络库</a></li><li class="dropdown-item"><!----> <a href="/pages/5f8c9f/" class="nav-link">Unix环境高级编程</a></li><li class="dropdown-item"><!----> <a href="/pages/3f1d21/" class="nav-link">Cpp提高编程</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="计算机基础" class="dropdown-title"><!----> <span class="title" style="display:;">计算机基础</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/7b1cb2/" class="nav-link">计算机网络</a></li><li class="dropdown-item"><!----> <a href="/pages/6048a8/" class="nav-link">操作系统</a></li><li class="dropdown-item"><!----> <a href="/pages/3b34ba/" class="nav-link">数据结构</a></li><li class="dropdown-item"><!----> <a href="/pages/412fe7/" class="nav-link">Linux</a></li><li class="dropdown-item"><!----> <a href="/pages/2dcfa1/" class="nav-link">算法</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="数据库" class="dropdown-title"><!----> <span class="title" style="display:;">数据库</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/efa3f2/" class="nav-link">基础篇</a></li><li class="dropdown-item"><!----> <a href="/pages/ccc445/" class="nav-link">MySql</a></li><li class="dropdown-item"><!----> <a href="/pages/54616e/" class="nav-link">Redis</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="嵌入式软件开发" class="dropdown-title"><!----> <span class="title" style="display:;">嵌入式软件开发</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d142c2/" class="nav-link">电子嵌入式通信协议</a></li><li class="dropdown-item"><!----> <a href="/pages/4c6bf3/" class="nav-link">深入浅出SSD</a></li><li class="dropdown-item"><!----> <a href="/pages/d3f36a/" class="nav-link">文件系统</a></li><li class="dropdown-item"><!----> <a href="/pages/e0cca7/" class="nav-link">汇编语言</a></li><li class="dropdown-item"><!----> <a href="/pages/fab2d7/" class="nav-link">STM32</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="开发日常" class="dropdown-title"><!----> <span class="title" style="display:;">开发日常</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/e472d1/" class="nav-link">随笔（持续更新）</a></li><li class="dropdown-item"><!----> <a href="/pages/71f6ae/" class="nav-link">Git知识总结</a></li><li class="dropdown-item"><!----> <a href="/pages/db6fb8/" class="nav-link">Git备忘清单</a></li><li class="dropdown-item"><!----> <a href="/pages/e1081f/" class="nav-link">Git 创建删除远程分支</a></li><li class="dropdown-item"><!----> <a href="/pages/777b8a/" class="nav-link">nvm使用小结</a></li><li class="dropdown-item"><!----> <a href="/pages/ee770e/" class="nav-link">虚拟机固定 IP 地址</a></li><li class="dropdown-item"><!----> <a href="/pages/1ab9a6/" class="nav-link">Shell 脚本学习笔记</a></li><li class="dropdown-item"><!----> <a href="/pages/411aa4/" class="nav-link">VScode 插件 CodeGeeX 使用教程</a></li><li class="dropdown-item"><!----> <a href="/pages/0d525d/" class="nav-link">KylinV10 将项目上传至 Github教程</a></li><li class="dropdown-item"><!----> <a href="/pages/907786/" class="nav-link">KylinV10 安装 MySQL 教程（可防踩雷）</a></li><li class="dropdown-item"><!----> <a href="/pages/a2d21e/" class="nav-link">kylinV10-SP1 安装 QT</a></li><li class="dropdown-item"><!----> <a href="/pages/b561cf/" class="nav-link">高并发内存池</a></li><li class="dropdown-item"><!----> <a href="/pages/6ab6d1/" class="nav-link">USBGUARD 项目编译环境配置</a></li><li class="dropdown-item"><!----> <a href="/pages/883f02/" class="nav-link">Power_Destory 项目</a></li><li class="dropdown-item"><!----> <a href="/pages/479472/" class="nav-link">U 盘清除工具编译教程</a></li><li class="dropdown-item"><!----> <a href="/pages/9c4241/" class="nav-link">个人博客代码推送教程</a></li><li class="dropdown-item"><!----> <a href="/pages/3ad765/" class="nav-link">SVN Trunk Branches的Merge操作</a></li><li class="dropdown-item"><!----> <a href="/pages/0c0ca8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端学习" class="dropdown-title"><!----> <span class="title" style="display:;">前端学习</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/99897f/" class="nav-link">HTML与CSS</a></li><li class="dropdown-item"><!----> <a href="/pages/51542d/" class="nav-link">JS学习</a></li><li class="dropdown-item"><!----> <a href="/pages/803f9d/" class="nav-link">Vue3入门</a></li><li class="dropdown-item"><!----> <a href="/pages/ca4cfb/" class="nav-link">Vue3进阶</a></li><li class="dropdown-item"><!----> <a href="/pages/50e8d3/" class="nav-link">黑马Vue3</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="MFC" class="dropdown-title"><!----> <span class="title" style="display:;">MFC</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/a4b108/" class="nav-link">MFC编程随记</a></li><li class="dropdown-item"><!----> <a href="/pages/41acbd/" class="nav-link">MFC实现ini配置文件的读取</a></li><li class="dropdown-item"><!----> <a href="/pages/951a7a/" class="nav-link">MFC实现点击列表头排序</a></li><li class="dropdown-item"><!----> <a href="/pages/a8598f/" class="nav-link">贴图法美化Button按钮</a></li><li class="dropdown-item"><!----> <a href="/pages/054516/" class="nav-link">MFC使用细节</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="闪存" class="dropdown-title"><!----> <span class="title" style="display:;">闪存</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/b925b8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li><li class="dropdown-item"><!----> <a href="/pages/28ec23/" class="nav-link">NAND Flash</a></li><li class="dropdown-item"><!----> <a href="/pages/62bf40/" class="nav-link">ARM 处理器</a></li><li class="dropdown-item"><!----> <a href="/pages/1a9374/" class="nav-link">嵌入式基础知识-存储器</a></li><li class="dropdown-item"><!----> <a href="/pages/aac5e3/" class="nav-link">闪存存储和制造技术概述</a></li><li class="dropdown-item"><!----> <a href="/pages/8f6056/" class="nav-link">芯片IO驱动力</a></li><li class="dropdown-item"><!----> <a href="/pages/d146b8/" class="nav-link">主流先进封装技术介绍</a></li><li class="dropdown-item"><!----> <a href="/pages/16f0ba/" class="nav-link">NAND Flash基础</a></li><li class="dropdown-item"><!----> <a href="/pages/90d8d0/" class="nav-link">基于PA算法的FTL引导</a></li><li class="dropdown-item"><!----> <a href="/pages/eb672b/" class="nav-link">SD逻辑擦除和物理擦除</a></li><li class="dropdown-item"><!----> <a href="/pages/747121/" class="nav-link">NAND Flash的SDR、ONFI、DDR接口</a></li><li class="dropdown-item"><!----> <a href="/pages/1eb351/" class="nav-link">【详解】Nand Flash必看知识</a></li><li class="dropdown-item"><!----> <a href="/pages/d2512a/" class="nav-link">【两万字详解】Nand Flash必看知识</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="面经" class="dropdown-title"><!----> <span class="title" style="display:;">面经</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d69946/" class="nav-link">虎牙C++技术面经</a></li><li class="dropdown-item"><!----> <a href="/pages/29251d/" class="nav-link">金山一面复习</a></li><li class="dropdown-item"><!----> <a href="/pages/c7c01f/" class="nav-link">完美世界秋招 C++ 游戏开发面经(Cpp部分)</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="其它" class="dropdown-title"><!----> <span class="title" style="display:;">其它</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/fa256e/" class="nav-link">博客搭建</a></li><li class="dropdown-item"><!----> <a href="/pages/335531/" class="nav-link">网站收藏箱</a></li></ul></div></div> <!----></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Cpp之旅</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/pages/c5bdd8/" class="sidebar-link">第1章 基础</a></li><li><a href="/pages/88a7db/" class="sidebar-link">第2章 用户自定义类型</a></li><li><a href="/pages/61ffe6/" aria-current="page" class="active sidebar-link">第3章 模块化</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/pages/61ffe6/#_3-1-分离编译" class="sidebar-link">3.1 分离编译</a></li><li class="sidebar-sub-header level2"><a href="/pages/61ffe6/#_3-2-模块" class="sidebar-link">3.2 模块</a></li><li class="sidebar-sub-header level2"><a href="/pages/61ffe6/#_3-3-模块与头文件两种方法的区别" class="sidebar-link">3.3 模块与头文件两种方法的区别</a></li><li class="sidebar-sub-header level2"><a href="/pages/61ffe6/#_3-4-命名空间" class="sidebar-link">3.4 命名空间</a></li><li class="sidebar-sub-header level2"><a href="/pages/61ffe6/#_3-5-函数参数与返回值" class="sidebar-link">3.5 函数参数与返回值</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/pages/61ffe6/#_3-5-1-结构化绑定" class="sidebar-link">3.5.1 结构化绑定</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/pages/61ffe6/#_3-6-建议" class="sidebar-link">3.6 建议</a></li></ul></li><li><a href="/pages/2dfe3d/" class="sidebar-link">第4章 错误处理</a></li><li><a href="/pages/1cb324/" class="sidebar-link">第5章 类</a></li><li><a href="/pages/fae683/" class="sidebar-link">第6章 基本操作</a></li><li><a href="/pages/2cdace/" class="sidebar-link">第7章 模板</a></li><li><a href="/pages/619376/" class="sidebar-link">第8章 概念和泛型编程</a></li><li><a href="/pages/48ac45/" class="sidebar-link">第9章 标准库</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Cpp专栏</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Effetcive_CPP</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>muduo网络库</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Unix环境高级编程</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Cpp提高编程</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><span data-v-06225672>CPP语言</span></li><li data-v-06225672><span data-v-06225672>Cpp之旅</span></li></ul> <div class="info" data-v-06225672><div title="作者" class="author iconfont icon-touxiang" data-v-06225672><a href="javascript:;" data-v-06225672>霜晨月</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-11-24</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">第3章 模块化<!----></h1> <!----> <div class="theme-vdoing-content content__default"><h1 id="cpp之旅-学习笔记-第3章-模块化"><a href="#cpp之旅-学习笔记-第3章-模块化" class="header-anchor">#</a> Cpp之旅（学习笔记）第3章 模块化</h1> <h2 id="_3-1-分离编译"><a href="#_3-1-分离编译" class="header-anchor">#</a> 3.1 分离编译</h2> <p>Cpp支持一种名为分离编译的概念，用户代码只能看见所用类型和函数的声明。</p> <p><strong>有两种方法可以实现它：</strong></p> <ul><li>头文件：将声明放进一个名为头文件的独立文件，然后将头文件以文本方式#include到代码中你需要声明的地方。</li> <li>模块：定义module文件，独立地编译它们，然后在需要时import它们。在import对应module时，只有其中显示export的声明是可见的。</li></ul> <p><strong>优点：</strong></p> <ul><li>可以尽可能地减少编译时间，并且强制要求程序中逻辑独立地部分分离开来（从而尽可能降低发生错误地概率）。</li></ul> <blockquote><p>模块技术是在Cpp20中出现地新特性，其提供了实质性地优势，对改善代码组织与编译耗时都有好处。</p></blockquote> <blockquote><p>一个单独编译的.cpp文件（包含它#include的.h文件）被称作一个翻译单元。</p></blockquote> <p><strong>使用#include及头文件实现模块化是一种传统方法，它具有明显地缺点：</strong></p> <ul><li><strong>编译时间：</strong> 如果你在101个翻译单元中#include header.h，这个header.h的头文件将被编译器处理101次。</li> <li><strong>依赖顺序：</strong> 如果你在header2.h之前#include header1.h，在header1.h中的定义与宏可能会影响header2.h中代码的含义，反之亦然。</li> <li><strong>不协调：</strong> 如果你在一个文件中定义一个实体，比如类型或者函数，然后在另一个文件中定义一个稍微不同的版本，则可能导致崩溃或者难以觉察的错误。</li> <li><strong>传染性：</strong> 所有表达头文件中某一个声明所需的代码，都必须出现在头文件中。这会导致代码膨胀，因为头文件为了完成声明需要#include其他头文件，这会导致头文件的用户需要（有意或者无意地）依赖头文件包含地实现细节。</li></ul> <h2 id="_3-2-模块"><a href="#_3-2-模块" class="header-anchor">#</a> 3.2 模块</h2> <p>Cpp20中出现了语言级的方式来直接实现模块化。</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">export</span> <span class="token keyword">module</span> <span class="token module">Vector</span><span class="token punctuation">;</span>			<span class="token comment">//定义一个module，名为Vector</span>
<span class="token keyword">export</span> <span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">double</span><span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">int</span> <span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">private</span><span class="token operator">:</span>
    <span class="token keyword">double</span><span class="token operator">*</span> elem<span class="token punctuation">;</span>				<span class="token comment">//elem指向一个数组，该数组包含sz个double类型的元素</span>
    <span class="token keyword">int</span> sz<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token class-name">Vector</span><span class="token double-colon punctuation">::</span><span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span> <span class="token operator">:</span> elem<span class="token punctuation">{</span><span class="token keyword">new</span> <span class="token keyword">double</span><span class="token punctuation">[</span>s<span class="token punctuation">]</span><span class="token punctuation">,</span> sz<span class="token punctuation">{</span>s<span class="token punctuation">}</span><span class="token punctuation">}</span> <span class="token punctuation">{</span><span class="token punctuation">}</span><span class="token comment">//初始化元素</span>
<span class="token keyword">double</span><span class="token operator">&amp;</span> Vector<span class="token double-colon punctuation">::</span><span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">return</span> elem<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> <span class="token class-name">Vector</span><span class="token double-colon punctuation">::</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> sz<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">export</span> <span class="token keyword">bool</span> <span class="token keyword">operator</span><span class="token operator">==</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> v1<span class="token punctuation">,</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> v2<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span><span class="token punctuation">(</span>v1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">!=</span> v2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
        <span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> v1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>v1<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">!=</span> v2<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span>
            <span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br><span class="line-number">25</span><br></div></div><p>上诉代码定义了一个 module，名为 Vector，这个模块导出了 Vector 类及所有成员函数，还有成员函数的操作符 ==。</p> <p>要使用上述 module，只要在需要用到它的地方 import 就可以了。</p> <p>例如：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token comment">//user.cpp</span>
<span class="token keyword">import</span> <span class="token module">Vector</span><span class="token punctuation">;</span>							<span class="token comment">//获得Vector的相关接口</span>
<span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string">&lt;cmath&gt;</span>						<span class="token comment">//获得标准库的数学函数接口，包含sqrt()</span></span>
<span class="token keyword">double</span> <span class="token function">sqrt_sum</span><span class="token punctuation">(</span>Vector<span class="token operator">&amp;</span> v<span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token keyword">double</span> sum <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">!=</span> v<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span>
        sum <span class="token operator">+=</span>std<span class="token double-colon punctuation">::</span><span class="token function">sqrt</span><span class="token punctuation">(</span>v<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>			<span class="token comment">//平方根之和</span>
    <span class="token keyword">return</span> sum<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p><code>#inclue &lt;cmath&gt;</code>也可以改为<code>import cmath;</code>这里仅仅是为了演示新旧方式的混合。</p> <h2 id="_3-3-模块与头文件两种方法的区别"><a href="#_3-3-模块与头文件两种方法的区别" class="header-anchor">#</a> 3.3 模块与头文件两种方法的区别</h2> <p><strong>头文件与模块的区别不仅仅是在语法上：</strong></p> <ul><li>模块只被编译一次，不会在每个用到它的翻译单元那里都被重新编译。</li> <li>两个模块 import 的顺序不影响其含义。</li> <li>如果你在模块内部 import 或者 #include 其他内容，模块的使用者不会隐式地获得那些模块地访问权：这意味着 import 没有传染性。</li> <li>模块在维护性与编译时间方面地改进非常显著。</li></ul> <div class="language- line-numbers-mode"><pre class="language-text"><code>例如：作者测试过使用 `import std;` 的 &quot;Hello，world!&quot; 程序
它的编译速度比使用 `#include&lt;iostream&gt;` 的版本 快10倍 
这还是在 std 模块因包含了整个标准库足足有 &lt;iostream&gt; 10 倍大小的前提下实现的。
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><p><strong>提升的原理：</strong></p> <ul><li>模块只导出接口，但头文件需要传递所有直接的或者间接的信息给编译器。</li></ul> <p><strong>不幸的是，module std还没有进入Cpp20。</strong> 附录A介绍了如何获得一份 module std 的方法，这里不详细展开。</p> <p><strong>示例：</strong></p> <p>当定义一个模块时，不需要将实现与声明分开写成两个文件，如果想改进你的源代码，可以这么做：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">export</span> <span class="token keyword">module</span> <span class="token module">Vector</span><span class="token punctuation">;</span>		<span class="token comment">//定义 module，名叫 Vector</span>
<span class="token keyword">export</span> <span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
    <span class="token comment">//...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword">export</span> <span class="token keyword">bool</span> <span class="token keyword">operator</span><span class="token operator">==</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> v1<span class="token punctuation">,</span> <span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> v2<span class="token punctuation">)</span><span class="token punctuation">{</span>
    <span class="token comment">//...</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><p>编译器负责把（用 export 指定的）模块的接口从实现细节中分离出来，因此，Vector 接口由编译器生成，不需要由用户指定。</p> <p>使用module时，不需要为了在接口文件内隐藏实现细节而将代码变得复杂；因为模块只导出显示export的声明。</p> <p>考虑如下代码：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">export</span> <span class="token keyword">module</span> <span class="token module">vector_printer</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token module">std</span><span class="token punctuation">;</span>
<span class="token keyword">export</span>
<span class="token keyword">template</span><span class="token operator">&lt;</span><span class="token keyword">typename</span> <span class="token class-name">T</span><span class="token operator">&gt;</span>
<span class="token keyword">void</span> <span class="token function">print</span><span class="token punctuation">(</span>std<span class="token double-colon punctuation">::</span>vector<span class="token operator">&lt;</span>T<span class="token operator">&gt;</span><span class="token operator">&amp;</span> v<span class="token punctuation">)</span>	<span class="token comment">//这是唯一能被用户看见的函数</span>
<span class="token punctuation">{</span>
    cout <span class="token operator">&lt;&lt;</span> <span class="token string">&quot;{\n&quot;</span><span class="token punctuation">;</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">const</span> T<span class="token operator">&amp;</span> val <span class="token operator">:</span> v<span class="token punctuation">)</span>
        std<span class="token double-colon punctuation">::</span>cout <span class="token operator">&lt;&lt;</span> <span class="token string">&quot; &quot;</span> <span class="token operator">&lt;&lt;</span> val <span class="token operator">&lt;&lt;</span> <span class="token char">'\n'</span><span class="token punctuation">;</span>
    cout <span class="token operator">&lt;&lt;</span> <span class="token char">'}'</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><h2 id="_3-4-命名空间"><a href="#_3-4-命名空间" class="header-anchor">#</a> 3.4 命名空间</h2> <ul><li>Cpp还提供了一种名为命名空间的机制，一方面表达某些声明是属于一个整体的，另一方面表面它们的名字不会与其他命名空间中的名字冲突。</li> <li>要想访问其他命名空间中的某个名字，最简单的方法是在这个名字前加上命名空间的名字作为限定（例如，std::cout和My_code::main）。</li> <li>”真正的main()“定义在全局命名空间中，换句话说，它不属于任何自定义的命名空间、类或者函数。</li> <li>如果觉得反复使用命名空间限定显得冗长及干扰了可读性，可以使用using声明将命名空间中的名字放进当前作用域。</li></ul> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">void</span> <span class="token function">my_code</span><span class="token punctuation">(</span>vector<span class="token operator">&lt;</span><span class="token keyword">int</span><span class="token operator">&gt;</span><span class="token operator">&amp;</span> x<span class="token punctuation">,</span>vector<span class="token operator">&lt;</span><span class="token keyword">int</span><span class="token operator">&gt;</span><span class="token operator">&amp;</span> y<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">using</span> std<span class="token double-colon punctuation">::</span>swap<span class="token punctuation">;</span> <span class="token comment">//将标准库的swap放进本地作用域</span>
    <span class="token comment">//...</span>
    <span class="token function">swap</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span>y<span class="token punctuation">)</span><span class="token punctuation">;</span>		 <span class="token comment">//std::swap()</span>
    other<span class="token double-colon punctuation">::</span><span class="token function">swap</span><span class="token punctuation">(</span>x<span class="token punctuation">,</span>y<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//某个其他的swap()</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><h2 id="_3-5-函数参数与返回值"><a href="#_3-5-函数参数与返回值" class="header-anchor">#</a> 3.5 函数参数与返回值</h2> <p>默认情况使用复制（传值），如果希望直接指向调用者环境中的对象，我们使用引用（传引用）的方式。</p> <p>从性能方面考虑，我们通常对小数据传值、对大数据传引用。这里的小意味着”复制开销很低“。通常而言，”尺寸在两到三个指针以内“是一个不错的标准。</p> <h3 id="_3-5-1-结构化绑定"><a href="#_3-5-1-结构化绑定" class="header-anchor">#</a> 3.5.1 结构化绑定</h3> <p>一个函数只能返回一个值，但这个值可以是拥有很多成员的类对象。这往往是函数体面地返回多个值地方法。</p> <p>例如：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">struct</span> <span class="token class-name">Entry</span> <span class="token punctuation">{</span>
    string name<span class="token punctuation">;</span>
    <span class="token keyword">int</span> value<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
Entry <span class="token function">read_entry</span><span class="token punctuation">(</span>istream<span class="token operator">&amp;</span> is<span class="token punctuation">)</span><span class="token comment">//简单地读函数</span>
<span class="token punctuation">{</span>
    string s<span class="token punctuation">;</span>
    <span class="token keyword">int</span> i<span class="token punctuation">;</span>
    is <span class="token operator">&gt;&gt;</span> s <span class="token operator">&gt;&gt;</span> i<span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token punctuation">{</span>s<span class="token punctuation">,</span>i<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">auto</span> e <span class="token operator">=</span> <span class="token function">read_entry</span><span class="token punctuation">(</span>cin<span class="token punctuation">)</span><span class="token punctuation">;</span>
cout <span class="token operator">&lt;&lt;</span> <span class="token string">&quot;{&quot;</span> <span class="token operator">&lt;&lt;</span> e<span class="token punctuation">.</span>name <span class="token operator">&lt;&lt;</span> <span class="token string">&quot;,&quot;</span> <span class="token operator">&lt;&lt;</span> e<span class="token punctuation">.</span>value <span class="token operator">&lt;&lt;</span> <span class="token string">&quot;}\n&quot;</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><p>在这里，{s,i}被用于构造Entry类型地返回值。类似地，我们也可以将Entry的成员”解包&quot;为局部变量：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">auto</span> <span class="token punctuation">[</span>n<span class="token punctuation">,</span>v<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token function">read_entry</span><span class="token punctuation">(</span>is<span class="token punctuation">)</span><span class="token punctuation">;</span>
cout <span class="token operator">&lt;&lt;</span> <span class="token string">&quot;{&quot;</span> <span class="token operator">&lt;&lt;</span> n <span class="token operator">&lt;&lt;</span> <span class="token string">&quot; , &quot;</span> <span class="token operator">&lt;&lt;</span> v <span class="token operator">&lt;&lt;</span> <span class="token string">&quot; }\n&quot;</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><p>这里的auto[n,v]声明了两个变量n和v，它们的类型来自对read_entry()返回类型的推导。</p> <p>这种把类对象成员的名称赋予局部变量名称的机制叫作结构化绑定。</p> <h2 id="_3-6-建议"><a href="#_3-6-建议" class="header-anchor">#</a> 3.6 建议</h2> <p>区分声明（用作接口）和定义（用作实现）；</p> <p>优先选择module而非头文件（在支持module的地方）；</p> <p>使用头文件描述接口、强调逻辑结构；</p> <p>在头文件中应避免定义非内联函数；</p> <p>不要在头文件中使用using指令；</p> <p>采用传值方式传递“小”值，采用传引用方式传递“大”值；</p> <p>优先选择传const引用方式而非传普通引用方式；</p> <p>不要过度使用返回类型推断；</p> <p>不要过度使用结构化绑定；使用命名的返回类型通常可以使代码更为清晰。</p></div></div> <!----> <div class="page-edit"><!----> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2024/6/3 14:54:44</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/88a7db/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">第2章 用户自定义类型</div></a> <a href="/pages/2dfe3d/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">第4章 错误处理</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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